Infographic: All the Ways to Detect an Exoplanet from Earth

There are billions of exoplanets in the known universe, but only a small fraction are detectable from Earth. Bodies outside of our solar system are so far away, we can only detect them using very indirect methods. Here are the primary ways scientists have discovered over a thousand exoplanets:

The most common and well-known method of detecting exoplanets is through a transit, or the point at which an exoplanet passes by a star from the perspective of an Earth-bound telescope. There's a slight decrease in the star's brightness during a transit, only by a small amount, but enough that astronomers can measure it. This is an extremely efficient method, as it allows astronomers to monitor many stars at one time, but it only works if the planet does, in fact, pass by its star as seen from Earth, and there's a high rate of false positives, up to 40%.

We can also observe when a massive planet's gravitational field causes a star to "wobble," or move back and forth towards and away from Earth. But this method is mostly effective for high-mass planets; for low-mass planets we can only observe the phenomenon approximately 160 light years away.

And finally, there's the gravitational lensing method, which is the only method of detecting the furthest exoplanets from Earth, up to tens of thousands of light years away. When there's a chance alignment between a nearby star and a faraway star, the nearby star acts as a lens illuminating the distant star. As a result, the brightness of the faraway exoplanet increases, making it visible to Earth for a brief time. Unfortunately, we'll only ever see these planets once, as gravitational microlensing events can't be repeated.